Upper motor neuron lesions (UMNL), which may be caused by neural disorders such as stroke, cerebrovascular accident, spinal cord injury, cerebral palsy, and/or traumatic brain injury, cause disability and paralysis in millions of people. Since the lower motor neuron system and muscles are generally intact in those with UMNL, muscle contractions may be evoked by directly applying electrical stimulus to the muscles via one or more electrodes. This technique, which may be used for rehabilitation and restoration of motor function, may be referred to as neuromuscular electrical stimulation (NMES). It may also be referred to as functional electrical stimulation (FES) when it is applied to produce a functional outcome, such as standing, cycling, and/or walking.
A number of challenges have been associated with development of NMES devices and methods, including the nonlinear response of muscle to electrical stimulation, load changes during functional movement, unexpected muscle spasticity, time lag between electrical stimulation and muscle force output, uncertainties in muscle physiology (e.g., temperature, pH, and/or architecture), and muscle fatigue.
One particular application of FES is FES-induced cycling. Since the 1980s, FES-induced cycling has been investigated as a safe means of exercise and rehabilitation for people with lower-limb paresis or paralysis, and numerous physiological benefits (e.g., improved cardiovascular health, increased muscle mass and bone mineral density, decreased spasticity, lower limb function) and psychological benefits (e.g., improved self-image, independence, socialization) have been reported. However, despite the reported benefits, FES-induced cycling generally has been metabolically inefficient and has resulted in low power output compared to volitional cycling by able-bodied individuals.
Improved devices and methods for application of electrical stimulation to a human body to produce functional outcomes, such as cycling, would be desirable.